1. Field of the Invention
The present invention relates generally to a method and apparatus for securing a connector employing a connecting body such as a ferrule over an inner member such as a wire. The present invention also has general application in making mechanically secure connections using connectors having a connecting body requiring shrinkage or mechanical deformation to be secured over an inner load carrying member, such as a guy wire or support cable. More specifically, but not by way of limitation, the present invention is directed to a method and apparatus for connecting ferrules such that the connected ferrule is substantially circular in shape but with sufficiently reduced cross-sectional area so as to achieve a circumferentially tight fit around the inner members.
2. Brief Description of Related Art
The field of wire termination utilizes a number of common practices to achieve electrically and mechanically efficient connections. In general, these practices involve some form of asymmetric deformation of a terminal ferrule around a group of wires. Prior art publications teach various forms of indentation of the ferrule, a general flattening of the ferrule, or a creasing, piercing, or buckling of the ferrule wall onto the inner members. The aforementioned methods create sharp and inconsistent deformations, indentations, and creases in the ferrule. In addition, the non-uniform shape of the reduced terminal creates voids between the terminal and the wires leading to possible fouling and corrosion from moisture migration into the voids. Still yet, the unpredictable variations formed by these methods of deformation create connections with equally unpredictable and inferior mechanical strength. Less common and more exotic methods do achieve symmetric connections such as hexagonal or square shapes, but still do not achieve finished connections having a substantially circular cross-section and thus suffer from the aforementioned problems to some degree.
It is more desirable to drive the finished ferrule into a near-circular shape. A number of advantages are achieved over methods using simple physical deformation to connect the ferrule. These advantages include excellent mechanical security and electrical conductivity; consistent mechanical pressure across the inner cross-section of the connection; an attractive appearance; no distress on inner wires or cable strands; no bending, cracking, tearing or piercing of ferrule walls; no exposed sharp edges of the ferrule to snag or foul in assembly; thickening and strengthening of the wall of the connected ferrule; and elimination of voids or gaps in the captured wire or cable thus removing points of entry for corrosive chemicals, liquids or gases.
U.S. Pat. No. 3,010,183, issued to E. W. Forney, Jr., on Nov. 28, 1961, discloses a crimping method in which a terminal ferrule is reduced in cross-sectional area without material change to its shape. The Forney patent further teaches a die set comprising a male die and a female die. The female die provides a die opening enlarged at its upper end and sharply tapering to a parallel section rounded at its lower end. The male die provides a curved surface of substantially the same radius of curvature as the rounded section at the bottom of the female die.
The method and apparatus of the Forney patent is fundamentally flawed in that the curved portions of the male and female dies have substantially equal radii of curvature. Using substantially equal radii of curvature introduce point loads and shear stresses between the lateral edges of the male die's curved face and the ferrule, such that the ferrule is sharply deformed at these points of contact as it is pushed into the opening of the female die. The point loads and shear stresses introduced by the apparatus of the Forney patent create sharp indentations and protrusions, materially changing the shape of the ferrule such that the smoothness and continuity of the outer surface is sacrificed. Using a substantially equal radius in the male die also creates extremely thin and fragile lateral edges along the width of the upper die. Exposing these edges to the forming pressures between the dies will cause them to break down and fail. In addition, the Forney patent diagrams a sharp transition within the tapering portion of the female die. It has been found in practice that pressing a ferrule into such a sharply tapering transition will cause it to bind and effectively jam the mechanism, damage the ferrule, and result in a failure to complete the forming process.